If I was starting with nothing and did not have an imminent need, I would look at truck (Snap-on, Cornwell, Matco and MAC) and industrial brands (Wright, SK, Bonney, Williams, Proto…) from garage/estate sales and flea markets.
Ideally, I like to pay around 10% or less of the retail prices. Obviously, gas and time make the real price higher.
On a long enough time line, you will have a ludicrous amount of the commonly found tools.
Once you figure out what the common tools are, you put the vast majority of your budget towards what you are not finding.
I live in a manufacturing area of a manufacturing metro area. There are a lot of chances to find cheap tools here. This, obviously, may not be true where you live. Another note would be that there are more pickers today than in years past. I started upgrading my tools from these sales about 16 years ago, and it was easier then. I have been building off the spoils of my first honey hole estate sale ever since.